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Staking Toroids on K2

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mussler

Staking Toroids on K2

All,
My K2, serial no. 05625 is complete and has been on the air for three
weeks today, but I'm still in the process of adding accessories. I've
mostly run it on 80 and 40 m with excellent results.

One question I have for the group- Has anyone found a need for
protecting the vertically mounted toroid inductors from mechanical shock
events during portable operations? If so, what staking material is
recommended? I am concerned about degrading exposed conductors with
anything I might use for an adhesive. I think the GE Silicone II
adhesive I have on hand is used for preventing corona or ionization
around high voltage terminals so maybe it would be a good candidate?

73
Mike Mussler
AI8Z
K2 serial 05625

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Don Wilhelm-3

RE: Staking Toroids on K2

Mike,

Use NOTHING to secure the toroids other than their leads. In the 7+ years
of the life of the K2, I have never heard of a failure die to a fractured
toroid lead, and there is one that I know of (I built it) that served for a
couple years as a mobile rig in the cab of an 18 wheeler - I am certain that
one saw more than normal shock and vibration.

Any securing compounds can cause damage - be particularly careful of the
silicone glues. The GE Silicone II that I have found smells like vinegar
and will cause a green corrosion mess when in contact with copper (could
even destroy the K2)

Elecraft recommends no fixatives for the toroids, and the use of them may
void the warranty, so go forth with it at your own peril.

73,
Don W3FPR

> -----Original Message-----
>
> All,
> My K2, serial no. 05625 is complete and has been on the air for three
> weeks today, but I'm still in the process of adding accessories. I've
> mostly run it on 80 and 40 m with excellent results.
>
> One question I have for the group- Has anyone found a need for
> protecting the vertically mounted toroid inductors from mechanical shock
> events during portable operations? If so, what staking material is
> recommended? I am concerned about degrading exposed conductors with
> anything I might use for an adhesive. I think the GE Silicone II
> adhesive I have on hand is used for preventing corona or ionization
> around high voltage terminals so maybe it would be a good candidate?
>
> 73
> Mike Mussler
> AI8Z
> K2 serial 05625
>

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.446 / Virus Database: 268.18.3/700 - Release Date: 2/24/2007
8:14 PM

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Jack Smith-6

Re: Staking Toroids on K2

Don:

I agree with you that nothing is required to secure the toroids to the
K2's PCB, it is not the case that a properly selected silicon compound
causes damage.

"Neutral cure" or "electronic grade" silicon will not cause damage, as
it sets up without emitting the acetic acid given off with the typical
RTV found in hardware stores. I ran tests last fall to determine the
effect of RTV upon Q and inductance of 4uH toroids, wound on T50-2 cores
for the Z10010 4.915 MHz bandpass filter I provide along with the Z90/91
panadapters, where the purchaser plans to use it with a K2. To the best
of my ability to read the HP4342A Q-meter, there were no changes in Q or
inductance after the neutral cure silicon rubber cured. The particular
product I used was a Dow-Corning compound, which gave off a faint smell
reminiscent of peppermint. About half the filters I built use it to
secure the toroids to the PCB. I abandoned it half-way into the
production run as (a) the wire leads, it turned out, were adequate and
(b) it was extremely difficult to apply without getting it all over the
PCB. I wound up doing post-assembly work with an Xacto knife, trimming
pieces of cured RTV from locations they did not belong.

I also ran tests to determine the effect of Q-dope on the same inductors
and found that the effects were somewhere between negligible and the
limit of my ability to measure. (For the newer hams, Q-dope is used to
secure windings to a coil form and is basically polystyrene dissolved in
toluene.) I decided to Q-dope the majority of the inductors I wound for
about 35 filters (140 total toroids) as method of assisting the long
term stability of the Z10010 filter, which is a bit touchy if the flat
nose and symmetrical flanks are to be maintained. A few filters were
assembled without Q-dope as a comparison, and they seem to work just as
well.

Still, as I said at the start of this message, I agree 100% with Don't
recommendations--don't use either RTV or Q-dope in your K2 assembly.

Jack K8ZOA
www.cliftonlaboratories.com

Don Wilhelm wrote:

> Mike,
>
> Use NOTHING to secure the toroids other than their leads. In the 7+ years
> of the life of the K2, I have never heard of a failure die to a fractured
> toroid lead, and there is one that I know of (I built it) that served for a
> couple years as a mobile rig in the cab of an 18 wheeler - I am certain that
> one saw more than normal shock and vibration.
>
> Any securing compounds can cause damage - be particularly careful of the
> silicone glues. The GE Silicone II that I have found smells like vinegar
> and will cause a green corrosion mess when in contact with copper (could
> even destroy the K2)
>
> Elecraft recommends no fixatives for the toroids, and the use of them may
> void the warranty, so go forth with it at your own peril.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> All,
>> My K2, serial no. 05625 is complete and has been on the air for three
>> weeks today, but I'm still in the process of adding accessories. I've
>> mostly run it on 80 and 40 m with excellent results.
>>
>> One question I have for the group- Has anyone found a need for
>> protecting the vertically mounted toroid inductors from mechanical shock
>> events during portable operations? If so, what staking material is
>> recommended? I am concerned about degrading exposed conductors with
>> anything I might use for an adhesive. I think the GE Silicone II
>> adhesive I have on hand is used for preventing corona or ionization
>> around high voltage terminals so maybe it would be a good candidate?
>>
>> 73
>> Mike Mussler
>> AI8Z
>> K2 serial 05625
>>
>>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.3/700 - Release Date: 2/24/2007
> 8:14 PM
>
> _______________________________________________
> Elecraft mailing list
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> Elecraft web page: http://www.elecraft.com
>
>

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Jack Smith-6

Re: Staking Toroids on K2

In reply to this post by mussler

Don:

The material I used is Dow-Corning 748, identified as a "non corrosive"
"food grade" product. If you find yourself in need of an
electronics-compatible sealant, I can recommend it. I ordered the D-C
748 from McMaster-Carr, and here's how they describe it:

*748 Noncorrosive— *Use where low odor is desirable. Bonds to metal,
plastic, glass, and rigid PVC. Resists moisture and weather and works
with corrosion-sensitive electrical and electronic equipment. Begins to
harden in 30 minutes. Temp. range is -67° to +350° F. Complies with FDA
regulation 21 CFR 177.2600 covering indirect food contact. UL listed.

A 3 ounce tube is $7.48, so you will pay quite a bit more than the
hardware store stuff, but it does exactly what you need in an electronic
sealant. There are other D-C electronic sealants with different
viscosity. The 748 is similar to standard RTV in viscosity and handling.

Jack K8ZOA
www.cliftonlaboratories.com

Don Wilhelm wrote:

> Jack,
>
> Thanks for the additional comments.
> The original post had specified the GE Silicone II adhesive that he
> had on hand. In my experience that is not a 'properly selected
> silicon compound'.
>
> The last tube I had of that I started to use on some terminals on an
> aluminum vertical - well I had a copper wire attached, and it turned a
> sickly green within two weeks. I had to scrape it all off (a tough
> job), use new hardware and wire. I vowed never to use any that was
> not specifically marked as 'electronic grade'.
>
> 73,
> Don W3FPR
>
> -----Original Message-----
>
> Don:
>
> I agree with you that nothing is required to secure the toroids
> to the K2's PCB, it is not the case that a properly selected
> silicon compound causes damage.
>
> "Neutral cure" or "electronic grade" silicon will not cause
> damage, as it sets up without emitting the acetic acid given off
> with the typical RTV found in hardware stores. I ran tests last
> fall to determine the effect of RTV upon Q and inductance of 4uH
> toroids, wound on T50-2 cores for the Z10010 4.915 MHz bandpass
> filter I provide along with the Z90/91 panadapters, where the
> purchaser plans to use it with a K2. To the best of my ability to
> read the HP4342A Q-meter, there were no changes in Q or inductance
> after the neutral cure silicon rubber cured. The particular
> product I used was a Dow-Corning compound, which gave off a faint
> smell reminiscent of peppermint. About half the filters I built
> use it to secure the toroids to the PCB. I abandoned it half-way
> into the production run as (a) the wire leads, it turned out, were
> adequate and (b) it was extremely difficult to apply without
> getting it all over the PCB. I wound up doing post-assembly work
> with an Xacto knife, trimming pieces of cured RTV from locations
> they did not belong.
>
> I also ran tests to determine the effect of Q-dope on the same
> inductors and found that the effects were somewhere between
> negligible and the limit of my ability to measure. (For the newer
> hams, Q-dope is used to secure windings to a coil form and is
> basically polystyrene dissolved in toluene.) I decided to Q-dope
> the majority of the inductors I wound for about 35 filters (140
> total toroids) as method of assisting the long term stability of
> the Z10010 filter, which is a bit touchy if the flat nose and
> symmetrical flanks are to be maintained. A few filters were
> assembled without Q-dope as a comparison, and they seem to work
> just as well.
>
> Still, as I said at the start of this message, I agree 100% with
> Don't recommendations--don't use either RTV or Q-dope in your K2
> assembly.
>
> Jack K8ZOA
> www.cliftonlaboratories.com
>
> Don Wilhelm wrote:
>> Mike,
>>
>> Use NOTHING to secure the toroids other than their leads. In the 7+ years
>> of the life of the K2, I have never heard of a failure die to a fractured
>> toroid lead, and there is one that I know of (I built it) that served for a
>> couple years as a mobile rig in the cab of an 18 wheeler - I am certain that
>> one saw more than normal shock and vibration.
>>
>> Any securing compounds can cause damage - be particularly careful of the
>> silicone glues. The GE Silicone II that I have found smells like vinegar
>> and will cause a green corrosion mess when in contact with copper (could
>> even destroy the K2)
>>
>> Elecraft recommends no fixatives for the toroids, and the use of them may
>> void the warranty, so go forth with it at your own peril.
>>
>> 73,
>> Don W3FPR
>>
>>
>>> -----Original Message-----
>>>
>>> All,
>>> My K2, serial no. 05625 is complete and has been on the air for three
>>> weeks today, but I'm still in the process of adding accessories. I've
>>> mostly run it on 80 and 40 m with excellent results.
>>>
>>> One question I have for the group- Has anyone found a need for
>>> protecting the vertically mounted toroid inductors from mechanical shock
>>> events during portable operations? If so, what staking material is
>>> recommended? I am concerned about degrading exposed conductors with
>>> anything I might use for an adhesive. I think the GE Silicone II
>>> adhesive I have on hand is used for preventing corona or ionization
>>> around high voltage terminals so maybe it would be a good candidate?
>>>
>>> 73
>>> Mike Mussler
>>> AI8Z
>>> K2 serial 05625
>>>
>>>
>> --
>> No virus found in this outgoing message.
>> Checked by AVG Free Edition.
>> Version: 7.5.446 / Virus Database: 268.18.3/700 - Release Date: 2/24/2007
>> 8:14 PM
>>
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>>
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
>

Jack Smith-6

Toroids - Effect of Winding Spacing on Inductance and Distributed Capacitance

Since toroid inductors are used throughout the K2, and since few other
topics generate as much discussion and the care and feeding of
toroid-wound inductors, I wanted to mention that Andy, G4OEP, has
recently completed an interesting study of the effect of turns spacing
upon inductance and distributed capacitance, which may be read at
http://g4oep.atspace.com/coil/coil.htm.

I also recommend Andy's other work, linked at his home page
http://g4oep.atspace.com/index.htm,

I've also added a new page to my site showing the effect of voltage on a
variety of ceramic capacitors.
http://www.cliftonlaboratories.com/capacitor_voltage_change.htm. It
provides at least a start of an answer to the question "when is a 0.1uF
capacitor not a 0.1uF capacitor"?

Jack K8ZOA
www.cliftonlaboratories.com

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Tom Zeltwanger

Re: Toroids - Effect of Winding Spacing on Inductance and Distributed Capacitance

Jack,

Sounds interesting but the link in your e-mail
(http://g4oep.atspace.com/coil/coil.htm) does not work for me.

Tom KG3V

Quoting Jack Smith <[hidden email]>:

> Since toroid inductors are used throughout the K2, and since few other
> topics generate as much discussion and the care and feeding of
> toroid-wound inductors, I wanted to mention that Andy, G4OEP, has
> recently completed an interesting study of the effect of turns spacing
> upon inductance and distributed capacitance, which may be read at
> http://g4oep.atspace.com/coil/coil.htm.
>
> I also recommend Andy's other work, linked at his home page
> http://g4oep.atspace.com/index.htm,
>
> I've also added a new page to my site showing the effect of voltage on a
> variety of ceramic capacitors.
> http://www.cliftonlaboratories.com/capacitor_voltage_change.htm. It
> provides at least a start of an answer to the question "when is a 0.1uF
> capacitor not a 0.1uF capacitor"?
>
> Jack K8ZOA
> www.cliftonlaboratories.com
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
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> Elecraft web page: http://www.elecraft.com
>

Ron D'Eau Claire-2

RE: Toroids - Effect of Winding Spacing on Inductance andDistributed Capacitance

The link doesn't work for me either.

There is a reason the Elecraft manuals clearly show the placement and
spacing of turns on the inductors. Unless the text says otherwise (such as
optimizing the output filter in the KX1) they should be wound just as shown:
spacing and number of turns. But it's not high precision work. If the coils
*look* like the pictures with about the right amount of core exposed in the
gap, and you have *exactly* the number of turns (counting the number of
times the wire passes through the center hole), the coil will work FB.

One mistake many builders make is in thinking the wire must lie tight
against the toroid core all the way around in each wrap, or turn. That's not
so. A small gap between the wire and core is fine. Indeed, it's preferable
to pulling the wire so tightly the enamel gets scrubbed off or the wire
breaks!

The second mistake is worrying too much about small breaks in the enamel
coating. The core is *not* conductive! Bare wire touching it is not a
problem. The problem is when two adjacent turns short out, usually where the
wire passes through the center hole, because bare copper on adjacent turns
touches. Not only can that cause trouble from the start, if it's a poor
contact between turns it can cause an intermittent that is very frustrating
to locate later. Again, don't be too aggressive about pulling the wire too
tight around the cores. Allow a natural, small, gap to form between the wire
and the core as you wind with moderate pressure on the wire.

Ron AC7AC

-----Original Message-----
Jack,

Sounds interesting but the link in your e-mail
(http://g4oep.atspace.com/coil/coil.htm) does not work for me.

Tom KG3V

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Jack Smith-6

Re: Toroids - Effect of Winding Spacing on Inductance andDistributed Capacitance

At the moment, I cannot reach his sub-pages either, and can only see
Andy's main page http://g4oep.atspace.com/index.htm from my locally
cached copy. I've had trouble in the past with connectivity on his page,
so I suggest trying again later.

As far as cores being non-conductive, that is true for powdered iron
(the typical red and yellow cores) but it is not necessarily true for
ferrite cores. The bulk resistivity of ferrite materials varies widely
from 1E9 down to 50 ohm-cm, and not all (few, actually in my limited
experience) ferrite cores are coated with a insulating surface. In
addition, many ferrite materials have an extremely high dielectric
constant, which suggests the need for a bit of spacing between the core
and the winding to reduce distributed capacitance arising from paths
through the core (obviously more important when the core is more
conductive.) Teflon tape has been used for this purpose. We should not,
of course, associate the term "toroid" with a particular core material,
as there is a world of difference between powdered iron and ferrite
materials, both of which are commonly available in a toroidal form.

There's also some degree of unit-to-unit variation in the core material,
both powdered iron and ferrite. I wound 140 4uH inductors last October
on T50-2 cores and measured every one for Q and inductance with an
HP4342A Q-meter. I found about a 10% difference in Q from the best to
the worst and around a 5% difference in inductance, to the point where I
had to wind more turns than the target and then measure and remove turns
to achieve my goal of 4uH +/- 2% with a minimum Q of 225 at 7.9 MHz. I
recall FairRite specs a 20% tolerance on permeability for its ferrite
materials, but my measurements suggest they actually are quite a bit
better than that. And, the majority of ferrite material is used in
applications where permeability tolerances are not critical, such as
broadband transformers and RFI suppression.

As far as following the instructions in the manual, I could not agree
more. If you follow the instructions it will work, absent the rare
defective component.

Jack K8ZOA

Ron D'Eau Claire wrote:

> The link doesn't work for me either.
>
> There is a reason the Elecraft manuals clearly show the placement and
> spacing of turns on the inductors. Unless the text says otherwise (such as
> optimizing the output filter in the KX1) they should be wound just as shown:
> spacing and number of turns. But it's not high precision work. If the coils
> *look* like the pictures with about the right amount of core exposed in the
> gap, and you have *exactly* the number of turns (counting the number of
> times the wire passes through the center hole), the coil will work FB.
>
> One mistake many builders make is in thinking the wire must lie tight
> against the toroid core all the way around in each wrap, or turn. That's not
> so. A small gap between the wire and core is fine. Indeed, it's preferable
> to pulling the wire so tightly the enamel gets scrubbed off or the wire
> breaks!
>
> The second mistake is worrying too much about small breaks in the enamel
> coating. The core is *not* conductive! Bare wire touching it is not a
> problem. The problem is when two adjacent turns short out, usually where the
> wire passes through the center hole, because bare copper on adjacent turns
> touches. Not only can that cause trouble from the start, if it's a poor
> contact between turns it can cause an intermittent that is very frustrating
> to locate later. Again, don't be too aggressive about pulling the wire too
> tight around the cores. Allow a natural, small, gap to form between the wire
> and the core as you wind with moderate pressure on the wire.
>
> Ron AC7AC
>
> -----Original Message-----
> Jack,
>
> Sounds interesting but the link in your e-mail
> (http://g4oep.atspace.com/coil/coil.htm) does not work for me.
>
> Tom KG3V
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

David Cutter

Re: Toroids - Effect of Winding Spacing on InductanceandDistributed Capacitance

Your comment about spacing off the core is interesting: my Drake AMU has an
attached balun which is constructed with the wire wound on a former which
stands the turns off the core. The wire is 1mm diameter bare wire and does
not touch at any point. I have never seen this anywhere else. The core is
also bare, ie no visible coating. I do not know its material.

David
G3UNA

----- Original Message -----
From: "Jack Smith" <[hidden email]>
To: "Ron D'Eau Claire" <[hidden email]>
Cc: <[hidden email]>
Sent: Monday, February 26, 2007 6:17 PM
Subject: Re: [Elecraft] Toroids - Effect of Winding Spacing on
InductanceandDistributed Capacitance

>
> As far as cores being non-conductive, that is true for powdered iron (the
> typical red and yellow cores) but it is not necessarily true for ferrite
> cores. The bulk resistivity of ferrite materials varies widely from 1E9
> down to 50 ohm-cm, and not all (few, actually in my limited experience)
> ferrite cores are coated with a insulating surface. In addition, many
> ferrite materials have an extremely high dielectric constant, which
> suggests the need for a bit of spacing between the core and the winding to
> reduce distributed capacitance arising from paths through the core
> (obviously more important when the core is more

Jack Smith-6

Re: Toroids - Effect of Winding Spacing on InductanceandDistributed Capacitance

David:

I have another message lost in the aether on the subject. I strongly
suspect the Drake tuner has a ferrite core balun. Ferrites can be
conductive, with a bulk resistivity ranging from 1E9 down to 50 ohm-cm,
depending on the material.

Hence if the balun is handling any degree of power, there may be a
significant turn-to-core voltage that causes arc-over. The voltage
turn-to-turn is less, of course, as the total voltage is more or less
evenly divided amongst all turns. But if the core has even moderate
conductivity, then the total voltage across the first and last turns
will appear between the first and last turns, insulated only by the wire
insulation.

Hence, spacing or wrapping the core is useful.

Jack K8ZOA

David Cutter wrote:

> Your comment about spacing off the core is interesting: my Drake AMU
> has an attached balun which is constructed with the wire wound on a
> former which stands the turns off the core. The wire is 1mm diameter
> bare wire and does not touch at any point. I have never seen this
> anywhere else. The core is also bare, ie no visible coating. I do
> not know its material.
>
> David
> G3UNA
>
> ----- Original Message ----- From: "Jack Smith"
> <[hidden email]>
> To: "Ron D'Eau Claire" <[hidden email]>
> Cc: <[hidden email]>
> Sent: Monday, February 26, 2007 6:17 PM
> Subject: Re: [Elecraft] Toroids - Effect of Winding Spacing on
> InductanceandDistributed Capacitance
>>
>> As far as cores being non-conductive, that is true for powdered iron
>> (the typical red and yellow cores) but it is not necessarily true for
>> ferrite cores. The bulk resistivity of ferrite materials varies
>> widely from 1E9 down to 50 ohm-cm, and not all (few, actually in my
>> limited experience) ferrite cores are coated with a insulating
>> surface. In addition, many ferrite materials have an extremely high
>> dielectric constant, which suggests the need for a bit of spacing
>> between the core and the winding to reduce distributed capacitance
>> arising from paths through the core (obviously more important when
>> the core is more
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

Jack Smith-6

Re: Toroids - Effect of Winding Spacing on Inductance andDistributed Capacitance

In reply to this post by Ron D'Eau Claire-2

Jack Smith-6

Toroids - Effect of Winding Spacing on Inductance andDistributed Capacitance

In reply to this post by Ron D'Eau Claire-2

I'm resending this post as it has not surfaced after a half hour. Slight
edits from first version.

At the moment, I cannot reach his sub-pages either, and can only see
Andy's main page http://g4oep.atspace.com/index.htm from my locally
cached copy. I've had trouble in the past with connectivity on his page,
so I suggest trying again later.

As far as cores being non-conductive, that is true for powdered iron
(the typical red and yellow cores) but it is not necessarily true for
ferrite cores. The bulk resistivity of ferrite materials varies widely
from 1E9 down to 50 ohm-cm, and not all (few, actually in my limited
experience) ferrite cores are coated with a insulating surface.
In
addition, many ferrite materials have an extremely high dielectric
constant, which suggests the need for a bit of spacing between the core
and the winding to reduce distributed capacitance arising from paths
through the core (obviously more important when the core is more
conductive.) Teflon tape has been used for this purpose. In addition, if
the core is conductive, then the total voltage across the winding
appears between the start and finish turns, so insulation or spacing may
be necessary to avoid rupturing the insulation.

We should not,
of course, associate the term "toroid" with a particular core material,
as there is a world of difference between powdered iron and ferrite
materials, both of which are commonly available in a toroidal form.

There's also some degree of unit-to-unit variation in the core material,
both powdered iron and ferrite. I wound 140 4uH inductors last October
on T50-2 cores and measured every one for Q and inductance with an
HP4342A Q-meter. I found about a 10% difference in Q from the best to
the worst and around a 5% difference in inductance, to the point where I
had to wind more turns than the target and then measure and remove turns
to achieve my goal of 4uH +/- 2% with a minimum Q of 225 at 7.9 MHz. I
recall FairRite specs a 20% tolerance on permeability for its ferrite
materials, but my measurements suggest they actually are quite a bit
better than that. And, the majority of ferrite material is used in
applications where permeability tolerances are not critical, such as
broadband transformers and RFI suppression.

As far as following the instructions in the manual, I could not agree
more. If you follow the instructions it will work, absent the rare
defective component.

Jack K8ZOA

Ron D'Eau Claire wrote:

Jack Smith-6

Toroids - Effect of Winding Spacing on Inductance andDistributed Capacitance

As of now (1600 EST), I can access Andy's sites.
http://g4oep.atspace.com/coil/coil.htm
http://g4oep.atspace.com/index.htm

Jack K8ZOA

>
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